Herpes simplex, in humans, exists as a latent infection. Once infected, the virus persists for the life of the host. Physical trauma, exposure to radiation, and suppression of adaptive immunity are all associated with reactivation of herpes simplex virus (HSV). On the other hand, most episodes of reactivation disease, have no known triggering event. Studies of humans with reactivation of herpes simplex virus reveal associations with genes important in the innate immune response; including both Toll Like Receptors (TLRs) and other proteins involved in the human innate immunity. A large study of patients with genital HSV revealed a highly significant association between TLR2 polymorphisms and frequency of reactivation. Another genetic analysis of patients with recurrent oral disease ("cold sores") revealed an association between TLRS and a very significant association with a polymorphism in an uncharacterized putative gene on chromosome 21 (which we have termed HELP (Herpes Emergence Limiting Protein). The level of antibodies to HSV was associated with a SNP in the TLR adapter protein MyD88. n this project the mechanism of association between TLR2 polymorphisms and genital reactivation between TLR3, HELP, and MyD88 and oral reactivation and antibody responses will be studied using peripheral blood cells challenged with HSV, and reconstitution of knockout cell lines with polymorphic variants of each gene. In addition, the relationship between the HELP gene and HSV will be defined using antibodies to the HELP protein for intracellular localization and a mouse model to define function. In collaboration with investigators from Project 1 and 2 the effects of different TLR and non-TLR genes will be evaluated in human cells. In collaboration with Project 3, we will test the hypothesis that certain virus strains are more likely than others to cause reactivation disease. RELEVANCE (See instructions): Herpes simplex causes lifelong disease in people. Certain genes have been associated with frequent "cold sores" (oral reactivation disease) and other genes have been associated with the development of genital herpes reactivation disease. This project will investigate the mechanism of these associations. The definition of these mechanisms is anticipated to lead to new ways to prevent reactivation and, perhaps, prevent herpes related diseases.